Refrigeration equipment for making ice on or within refrigerated tubes has been know for many years. In my U.S. Pat. No. 4,185,467 defrosting to free the ice is done by relatively warm liquid refrigerant.
In Nilsson et al U.S. Pat. No. 3,759,061, gaseous refrigerant for defrosting is brought into a compartment at the lower ends of the ice filled tubes but prior thereto the liquid refrigerant around the tubes is removed.
Other patents in the art include Williams, Jr. No. 2,618,129; Brandin et al No. 2,721,452; Kara No. 3,803,871; Chapman No. 2,807,152, 2,739,457 and 2,807,150; Kocher No. 3,053,058; Lowe No. 3,280,585; Gordon No. 3,769,812; Hammer No. 4,094,168; Nilsson et al No. 3,206,945; Kubaugh No. 2,239,234; and Dixon No. 3,435,633.